This invention relates generally to the field of telephony, and more particularly to an improved main distributing frame used in telephone offices for the interconnection of individual cable pairs to switching equipment. Main distributing frames of this general type are well known in the art, and the invention lies in specific constructional details which simplify manufacture, improve space utilization, and lower maintenance expenses due to the use of short jumpers, single-sided configuration, and other advantages, as compared with conventional distributing frames.
With the constant growth of subscribers in a given telephone office, the problem of accommodation of ever-growing connector pairs is constant. The known art includes many forms of main frames adapted to provide high space utilization with maximum connector pair density, while still providing adequate accessibility for servicing. To obtain such advantages, it is customary to provide connector blocks in which availability of terminals is possible only by providing protector terminals on one side of the frame and connector terminals on the opposite side. It follows that a corridor must be provided to allow accessibility to each side of the frame. While it is, of course, possible to have a plurality of such frames disposed upon a plant floor in mutually parallel relation, such arrangement precludes maximum space utilization possible by mounting frames against vertical walls or other areas where accessibility on one side only is possible. In the case of two-sided frames, expansion in co-planar fashion is difficult because of the lack of troughs and passages for jumpering and the accompanying difficulty of tracing connections.
In our prior patent, with Albert Atun, U.S. Pat. No. 4,117,273, granted Sept. 26, 1978, and assigned to the same assignee as the instant application, there is disclosed an improved single-sided frame in which some of the above mentioned problems are ameliorated to some degree by the provision of structure in which connections and protector blocks are positioned over a forward surface of the frame such that the exposed surfaces of the blocks are parallel to the plane of the frame, and the rear of the frame is provided with a large number of horizontal troughs which cooperate with a relatively fewer number of vertical troughs to accomplish horizontal and vertical jumpering. Using such construction, the rear surface of the frames are wired before the frames are positioned against a wall or other structure, and subsequent servicing is afforded only on the forward or exposed surface of the frames. While these constructions constituted an improvement over conventional main frame structure, a relatively large number of both vertical and horizontal cable-carrying troughs are required, which occupy space, and prevent the utilization of such space for the mounting of terminal blocks of one type or another. Additionally, in some installation situations, it is not always possible to prewire the rear surface of the frame in such manner as to preclude the possibility of future access.